Many people develop back pain during the course of their life due to traumatic injury, disease, or genetic defect. Typically, the patients' intervertebral discs, which support the spine, are damaged, causing the discs to bulge or herniate. The disc bulge then impinges on the nerves of the spine and cause back pain. Surgeons often perform a discectomy to trim the disc bulge to alleviate back pain. However, the discectomy may structurally weaken the disc and often leads to subsequent structural failure of the disc due to wear and aging, once again causing impingement on the nerves of the spine and cause back pain. Surgical implantation of a medical implant device to structurally support and separate the vertebrae may become desirable to end debilitating back pain and allow patients to regain normal life activities.
One currently accepted practice is to use natural bone from the patient (i.e., autograft) or cadaver bone donated by organ donors (i.e. sterilized allograft), as a material to structurally support and separate the vertebrae. While natural bone implants advantageously promote bone growth and fusion at the implant site, the use of natural bone can be problematic because of the potential for structural failure of the implant, rejection of the implant by the patient, and the risk of infection.
In particular, failure of the bone graft implant may be caused by non-viability of the bone graft material, which allows for accumulation of structural micro-damage. In addition, the quality of the bone graft greatly depends on the health and age of the bone donor, which results in highly variable quality in bone graft. Failure of the implant can also result from rejection of the implant by the patient's immune system. In addition, the risk of infection from cadaver bone creates many attendant costs of mitigation. The potential for implant failure, rejection, and/or infection may necessitate numerous painful revision surgeries.
In view of the problems associated with natural bone implants, vertebral body replacement devices (“VBRs”) are often made of strong and non-brittle biocompatible materials, such as carbon fiber, titanium, and/or materials of the polyaryletherketone family, including, for example, PEEK (polyetheretherketone), PAEK (polyaryletherketone), PEK (polyetherketone), PEKK (polyetherketoneketone), PEKEKK (polyetherketoneetherketoneketone), PEEKK (polyetheretherketoneketone), and PAEEK (polyaryletheretherketone), and any combination thereof.
VBRs commonly have generally annular bodies including relatively large, central throughbores in which bone graft material can be packed to encourage bony ingrowth through the throughbore. Other smaller openings, apertures and/or channels can also be provided in the implant for allowing bone ingrowth and/or for cooperating with corresponding engagement members of an insertion tool for inserting the VBR between vertebrae. In this regard, during VBR insertion there generally are very high forces generated at the interface between the engagement members of the insertion tool and the surfaces about the VBR body openings in which the engagement members are fit. VBRs formed of a material such as PEEK are advantageously strong and ductile to minimize damage to the implant body during insertion. However, such materials are not bioresorbable and do not allow bone growth through the implant body itself. Moreover, should a revision surgery be required, the implant must be removed with particular care given to ensure there is not remaining debris.
Bioactive bioceramic materials, such as hydroxyapatite (HA) and tricalcium (TCP) phosphate are attractive and widely utilized materials for orthopedic and dental implants. A “bioactive” material is one that elicits a specific biological response at its surface, which results in a beneficial biological and chemical reaction with the surrounding tissue. These reactions lead to chemical and biological bonding to the tissue at the interface between tissue and the bioactive implant, rather than mere ingrowth of tissue into pores of the implant, which only provide mechanical fixation. HA has been of particular interest in orthopedic and dental application because the composition closely resembles native bone mineral and is inherently bioactive and osteoconductive. However, because such calcium phosphate bioceramic implants have low reliability under tensile loads, such materials have generally only been used as powders, or as small, unloaded implants such as in the middle ear, dental implants with reinforcing metal posts, coatings on metal implants, low-loaded porous implants where bone growth acts as a reinforcing phase, and as the bioactive phase in a composite implant.
Thus, it would be advantageous to provide an implant device for implantation in the intervertebral space between vertebral bodies for supporting and/or spacing apart the vertebral bodies and promoting bone growth and fusion therebetween and/or immobilization thereof. It would further be advantageous to provide such an implant device formed of a material that provides the strength and stability, while also being bioresorbable and promoting bone growth therein. The present invention may be used to fulfill these needs, as well as other needs and benefits, as will be apparent from the following description of embodiments of the present invention.